Silicon dioxide (SiO2) has been used as the primary gate-dielectric material in field effect devices for almost 50 years. However, it is projected, for example, that metal oxide semiconductor (MOS) field effect transistors (FETs) will have gate lengths of less than about 10 nanometers (nm) and will require equivalent oxide thicknesses of SiO2 of about 0.5 nm or less than about 3 atomic layers. The minimum equivalent oxide thickness of SiO2 has been estimated to be about 0.7 nm. Such thin oxide layers represent a fundamental challenge to the historic steady reduction in integrated circuit sizes that have characterized the very successful semiconductor industry. Specifically, at these small thicknesses, the amount of current leakage, which is caused by direct tunneling of charge carriers through the thin oxide layer, may be too high.
Since the capacitance of the oxide layer is proportional to the dielectric constant and inversely proportional to its thickness, using a higher dielectric constant material allows a proportionally greater thickness to be used. High dielectric-constant (high-k) materials, or materials having a dielectric constant greater than that of SiO2 (i.e., 3.9), are clearly needed for silicon (Si) based MOS technologies since the above equivalent oxide thickness are too small to be practically implemented with SiO2. High-k insulators, or high-k dielectrics, are needed to compensate for gate current increases that result from the scaling down of gate oxide thicknesses. Such dielectrics are even more important for low-power circuits where gate leakage power consumption represents a fundamental limitation.
One approach to implementing high-k dielectrics is to use oxides of hafnium (e.g., HfO2), tantalum (e.g., Ta2O5), lanthanum (e.g., La2O3), and zirconium (e.g., ZrO2) or nitrides of hafnium (e.g., HfSiON) or tantalum (e.g., TaN). The dielectric constants of these amorphous materials are about 5 to about 20. These materials in their current implementation, however, have reliability issues associated with them. Specifically, charge trapping effects can cause transistor degradation, and channel carrier mobility and transconductance may be degraded. Stacks or laminates of these oxides may provide improved performance. However, since stacked layers may be represented as capacitors in series, the equivalent oxide thickness will never be less than that of the lowest dielectric constant layer.
Accordingly, there is a need for improved high-k materials, high-k electrical devices manufactured therefrom, and associated fabrication methods that exhibit a suitably small effective oxide thickness as well as good stability and reliability on the substrate. It is to the provision of such materials, devices, and methods that the various embodiments of the present invention are directed.